Trial spawners that spawn slimes open early

When killing the slimes that the spawner spawns, it only checks for the slimes it directly spawns, not the smaller ones created once the large and medium slimes are killed

Slime bug report.mp4 (Sorry for low video quality)

Steps to reproduce -

1 - Find a trial spawner that spawns slimes
2 - Kill the slimes that the spawner directly spawns, not the smaller ones created by killing the bigger slimes
3 - The trial spawner will open while the smaller slimes are still alive

While I don't know the code behind this, I believe what happened here is the spawner only checks to see if the mobs the spawner has spawned have been killed. A possible solution to this bug could be to pass down data from the larger slime to all of the smaller slimes it spawns when killed.